Four years after Congress put the federal government in charge of aviation security, it is about to change course and encourage private security companies to run airport checkpoints.

Lawmakers agreed Thursday to give airports legal protection if they get rid of federal screeners and replace them with private companies. The agreement was reached by a bipartisan committee of House and Senate negotiators after Rep. Hal Rogers, R-Ky., put the lawsuit protection in the final version of the Homeland Security Department's 2006 spending bill.

Twenty to 30 airports have balked at switching to private screeners because they feared being named in lawsuits that might arise from a terror incident, airport lobbyist Stephen Van Beek said.

Lawsuit protection "is a big move," Van Beek said.

Private companies can deploy screeners more efficiently than the federal Transportation Security Administration, Van Beek said, and hire them more quickly to avoid staffing shortages that close checkpoint lanes.

Some Democrats said the law that put the federal government in charge of aviation security after the 9/11 attacks was intended to discourage airports from using private screeners.

"If they (airports) want to bring in the private vendors, I think they need to provide their own insurance," said Rep. Peter DeFazio, D-Ore.

The push for legal protection began over the summer when San Francisco International Airport said it would stop using a private security company because of lawsuit concerns. The airport is the largest in a pilot program testing whether private companies do a better job than federal screeners. "We're very, very pleased," said Peter Nardoza, lobbyist for the San Francisco airport, which decided to continue using a private company.

The TSA hires and regulates security companies that staff airport checkpoints. Private screeners undergo the same training and background scrutiny as their TSA counterparts and must receive at least as much in wages and benefits.

Van Beek, the airport lobbyist, said screening companies didn't have such oversight before the Sept. 11 attacks. "Accountability is a lot higher," he said.

Vincent said he fears federal oversight and funding will wane over time, "diminishing the security improvements since 9/11."